3d memory semiconductor devices and structures

ABSTRACT

A 3D memory device, the device including: a plurality of memory cells, where each memory cell of the plurality of memory cells includes at least one memory transistor, where each of the at least one memory transistor includes a source, a drain, and a channel; and a plurality of bit-line pillars, where each bit-line pillar of the plurality of bit-line pillars is directly connected to a plurality of the source or the drain, where the bit-line pillars are vertically oriented, where the channel is horizontally oriented, and where the channel is isolated from another channel disposed directly above the channel.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This application relates to the general field of Integrated Circuit (IC)devices and fabrication methods, and more particularly to multilayer orThree Dimensional Integrated Memory Circuit (3D-Memory) and ThreeDimensional Integrated Logic Circuit (3D-Logic) devices and fabricationmethods.

2. Discussion of Background Art

Over the past 40 years, there has been a dramatic increase infunctionality and performance of Integrated Circuits (ICs). This haslargely been due to the phenomenon of “scaling”; i.e., component sizessuch as lateral and vertical dimensions within ICs have been reduced(“scaled”) with every successive generation of technology. There are twomain classes of components in Complementary Metal Oxide Semiconductor(CMOS) ICs, namely transistors and wires. With “scaling”, transistorperformance and density typically improve and this has contributed tothe previously-mentioned increases in IC performance and functionality.However, wires (interconnects) that connect together transistors degradein performance with “scaling”. The situation today is that wiresdominate the performance, functionality and power consumption of ICs.

3D stacking of semiconductor devices or chips is one avenue to tacklethe wire issues. By arranging transistors in 3 dimensions instead of 2dimensions (as was the case in the 1990s), the transistors in ICs can beplaced closer to each other. This reduces wire lengths and keeps wiringdelay low and wire.

There are many techniques to construct 3D stacked integrated circuits orchips including:

-   -   Through-silicon via (TSV) technology: Multiple layers of dice        are constructed separately. Following this, they can be bonded        to each other and connected to each other with through-silicon        vias (TSVs).    -   Monolithic 3D technology: With this approach, multiple layers of        transistors and wires can be monolithically constructed. Some        monolithic 3D and 3DIC approaches are described in U.S. Pat.        Nos. 8,273,610, 8,298,875, 8,362,482, 8,378,715, 8,379,458,        8,450,804, 8,557,632, 8,574,929, 8,581,349, 8,642,416,        8,669,778, 8,674,470, 8,687,399, 8,742,476, 8,803,206,        8,836,073, 8,902,663, 8,994,404, 9,023,688, 9,029,173,        9,030,858, 9,117,749, 9,142,553, 9,219,005, 9,385,058,        9,406,670, 9,460,978, 9,509,313, 9,640,531, 9,691,760,        9,711,407, 9,721,927, 9,799,761, 9,871,034, 9,953,870,        9,953,994, 10,014,292, 10,014,318, 10,515,981, 10,892,016; and        pending U.S. Patent Application Publications and applications,        Ser. Nos. 14/642,724, 15/150,395, 15/173,686, 16/337,665,        16/558,304, 16/649,660, 16/836,659, 17/151,867, 62/651,722;        62/681,249, 62/713,345, 62/770,751, 62/952,222, 62/824,288,        63/075,067, 63/091,307, 63/115,000, 2020/0013791, 16/558,304;        and PCT Applications (and Publications): PCT/US2010/052093,        PCT/US2011/042071 (WO2012/015550), PCT/US2016/52726        (WO2017053329), PCT/US2017/052359 (WO2018/071143),        PCT/US2018/016759 (WO2018144957), and PCT/US2018/52332(WO        2019/060798). The entire contents of the foregoing patents,        publications, and applications are incorporated herein by        reference.    -   Electro-Optics: There is also work done for integrated        monolithic 3D including layers of different crystals, such as        U.S. Pat. Nos. 8,283,215, 8,163,581, 8,753,913, 8,823,122,        9,197,804, 9,419,031, 9,941,319, 10,679,977, and 10,943,934. The        entire contents of the foregoing patents, publications, and        applications are incorporated herein by reference.    -   In addition, the entire contents of U.S. patents; U.S. Pat. Nos.        11,018,156, 10,892,016, 10,622,365, 10,297,599, 9,953,994;        application Ser. Nos. 17/235,879, 63,091,307, 63,075,067,        62/952,222, 62/897,364, 62/856,732, and 62/831,080 are        incorporated herein by reference.

Additionally the 3D technology according to some embodiments of theinvention may enable some very innovative IC devices alternatives withreduced development costs, novel and simpler process flows, increasedyield, and other illustrative benefits.

SUMMARY

The invention relates to multilayer or Three Dimensional IntegratedCircuit (3D IC) devices and fabrication methods. Important aspects of 3DIC are technologies that allow layer transfer. These technologiesinclude technologies that support reuse of the donor wafer, andtechnologies that support fabrication of active devices on thetransferred layer to be transferred with it.

In one aspect, a 3D memory device, the device including: a plurality ofmemory cells, where each of the plurality of memory cells includes atleast one memory transistor, where each of the at least one memorytransistor includes a source, a drain and a channel; a plurality ofbit-line pillars, where each of the plurality of bit-line pillars isdirectly connected to a plurality of the source or the drain, where thebit-line pillars are vertically oriented, where the channel ishorizontally oriented, and where the channel includes a circular shapeor an ellipsoidal shape.

In another aspect, a 3D memory device, the device including: a pluralityof memory cells, where each of the plurality of memory cells includes atleast one memory transistor, where each of the at least one memorytransistor includes a source, a drain and a channel; a plurality ofbit-line pillars, where each of the plurality of bit-line pillars isdirectly connected to a plurality of the source or the drain, where thebit-line pillars are vertically oriented, and where the channel ishorizontally oriented and includes a channel width longer than 5 nm andshorter than 25 nm.

And in another aspect, a 3D memory device, the device including: aplurality of memory cells, where each of the plurality of memory cellsincludes at least one memory transistor, where each of the at least onememory transistor includes a source, a drain and a channel; a pluralityof bit-line pillars, where each of the plurality of bit-line pillars isdirectly connected to a plurality of the source or the drain, where thebit-line pillars are vertically oriented, where at least one of theplurality of the memory cells include a tunneling oxide thinner than 1nm, and where at least one of the plurality of the memory cells includea tunneling oxide thicker than 3 nm.

And in another aspect, a 3D memory device, the device including: aplurality of memory cells, where each of the plurality of memory cellsincludes at least one memory transistor, where each of the at least onememory transistor includes a source and a drain; a plurality of bit-linepillars, where each of the plurality of bit-line pillars is directlyconnected to a plurality of the source or the drain, where each of theplurality of bit-line pillars includes metal atoms such that theplurality of bit-line pillars have at least partial metallic properties;and a thermal path from the bit-line pillars to an external surface ofthe device to remove heat.

And in another aspect, a 3D memory device, the device including: aplurality of memory cells, where each of the plurality of memory cellsincludes at least one memory transistor, where each of the at least onememory transistor includes a source and a drain; a plurality of bit-linepillars, where each of the bit-line pillars is directly connected to aplurality of the source or the drain; and a thermal path from thebit-line pillars to an external surface of the device to remove heat.

And in another aspect, a 3D memory device, the device including: aplurality of memory cells, where each of the plurality of memory cellsincludes at least one memory transistor, where each of the at least onememory transistor includes a source, a channel and a drain; and aplurality of bit-line pillars, where each of the bit-line pillars isdirectly connected to a plurality of the sources or drains, where thechannel includes crystallized polysilicon, and where the crystallizedpolysilicon has been crystallized from a heat sourced from the source ordrain of the channel.

And in another aspect, a 3D memory device, the device including: aplurality of memory cells, where each memory cell of the plurality ofmemory cells includes at least one memory transistor, where each of theat least one memory transistor includes a source, a drain, and achannel; and a plurality of bit-line pillars, where each bit-line pillarof the plurality of bit-line pillars is directly connected to aplurality of the source or the drain, where the bit-line pillars arevertically oriented, where the channel is horizontally oriented, andwhere the channel is isolated from another channel disposed directlyabove the channel.

And in another aspect, a 3D memory device, the device including: aplurality of memory cells, where each memory cell of the plurality ofmemory cells includes at least one memory transistor, where each of theat least one memory transistor includes a source, a drain, and achannel; and a plurality of bit-line pillars, where each bit-line pillarof the plurality of bit-line pillars is directly connected to aplurality of the source or the drain, where the bit-line pillars arevertically oriented, and where the plurality of memory cells include apartially or fully metalized source, and/or a partially or fullymetalized drain.

And in another aspect, a 3D memory device, the device including: aplurality of memory cells, where each memory cell of the plurality ofmemory cells includes at least one memory transistor, where each of theat least one memory transistor includes a source, a drain, and achannel; and a plurality of bit-line pillars, where each bit-line pillarof the plurality of bit-line pillars is directly connected to aplurality of the source or the drain, where the bit-line pillars arevertically oriented, and where the channel includes crystallizedpolysilicon.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will be understood and appreciatedmore fully from the following detailed description, taken in conjunctionwith the drawings in which:

FIGS. 1A-1H are exemplary illustrations of some of the process steps toform a 3D NOR structure;

FIGS. 1I-1L are exemplary illustrations via a planar view of a 3D NORstructure;

FIGS. 1M-1Q are exemplary illustrations of alternative process steps toform a 3D NOR structure;

FIG. 2 is example of periphery under and periphery over a 3D NORstructure;

FIGS. 3A-3B are examples of back-gate bias control schemes;

FIG. 4A is an example of a word line select structure;

FIG. 4B is an additional example of a back-gate bias control scheme:

FIGS. 5A and 5B are exemplary illustrations of a memory cell write andread operation scheme;

FIG. 5C is an exemplary illustration of a programmed and erased memorycell Id-Vg characteristics;

FIG. 5D is an exemplary illustration of a write scheme for mirror-bitoperation of a memory cell;

FIG. 5E is an exemplary illustration of a read scheme for mirror-bitoperation of a memory cell;

FIG. 6A is an exemplary illustration of a transfer curve of a chargetrap memory cell;

FIG. 6B is an exemplary illustration of an operational method for acharge trap memory;

FIGS. 6C-6E are exemplary illustrations of the effects of a trappre-saturation operation;

FIGS. 6F and 6G are exemplary illustrations of a pre-saturation modecharge trap memory threshold detection delta V;

FIGS. 7A and 7B are exemplary illustrations of some of the advantages ofmetallic bit lines in a 3D NOR-P structure and device;

FIG. 8 is an exemplary illustration of various options for reading a 3DNOR-P device or structure; and

FIGS. 9A-9C are exemplary illustrations of array options with SL/BLselect transistors under the 3D-NOR memory array.

DETAILED DESCRIPTION

An embodiment of the invention is now described with reference to thedrawing figures. Persons of ordinary skill in the art will appreciatethat the description and figures illustrate rather than limit theinvention and that in general the figures are not drawn to scale forclarity of presentation. Such skilled persons will also realize thatmany more embodiments are possible by applying the inventive principlescontained herein and that such embodiments fall within the scope of theinvention which is not to be limited except by any appended claims.

Some drawing figures may describe process flows for building devices.The process flows, which may be a sequence of steps for building adevice, may have many structures, numerals and labels that may be commonbetween two or more adjacent steps. In such cases, some labels, numeralsand structures used for a certain step's figure may have been describedin the previous steps' figures.

The use of layer transfer in the construction of a 3D IC based systemcould enable heterogeneous integration wherein each strata/layer/levelmay include, for example, one or more of MEMS sensor, image sensor, CMOSSoC, volatile memory such as DRAM and SRAM, persistent memory, andnon-volatile memory such as Flash, RRAM, FRAM, HRAM, MRAM, and OTP. Suchcould include adding memory control circuits, also known as peripheralcircuits, on top or below a memory array. The memory strata may containonly memory cells but not control logic, thus the control logic may beincluded on a separate stratum. Alternatively, the memory strata maycontain memory cells and simple control logic where the control logic onthat stratum may include at least one of decoder, buffer memory, senseamplifier. The circuits may include the charge pumps and high voltagetransistors, which could be made on a strata using silicon transistorsor other transistor types (such as SiGe, Ge, CNT, etc.) using amanufacturing process line that may be, and often is, different than thelow voltage control circuit manufacturing process line. The analogcircuits, such as for the sense amplifiers, and other sensitive linearcircuits could also be processed independently and be transferred overto the 3D fabric. Such 3D construction could include “Smart Alignment”techniques presented in this invention or incorporated references, orleverage the repeating nature of the memory array to reduce the impactof the wafer bonder misalignment on the effectiveness of theintegration; such as is presented in at least PCT/US2017/052359(WO2018/071143), incorporated herein by reference in its entirety,particularly in respect to its FIG. 11A to FIG. 12J, or using hybridbonding techniques as presented in respect to its FIG. 20A to FIG. 25J.

More specifically, at least within PCT/US2018/016759, published asWO2018/144957, various 3D memory structures are presented including astructure named 3D NOR-P such as in respect to at least FIGS. 11A-22D,and FIGS. 27A-34C, and enhancements as presented in at leastPCT/US2018/52332, published as WO 2019/060798, such as in respect toFIGS. 9A-13A, and FIGS. 14A-18, all of the foregoing is incorporatedherein by reference in its entirety. Much of the following are furthervariations, enhancements, and detailed alternatives for such a 3D NOR-Pmemory structure, device and manufacturing methods.

An alternative process flow for such a 3D NOR-P structure is presentedin reference to FIGS. 1A-1H. These are 3D illustrations along X-Y-Zdirection 100, in which X-Y directions are along the plane of the waferand Z direction is perpendicular to the wafer front/top surface. The 3DNOR-P structure can be hereinafter cited as 3D memory array or 3D array,interchangeably. The base structure starts with a preprocessed waferincluding foundation structure 108, which sometimes is referenced asperiphery under cell (“PUC”) or cell over periphery (“COP”). Thefoundation structure 108 could include various circuits, for example,such as decoder, sense amplifier, data buffer, address buffer,interconnect matrices/structures with or without antifuses, I/O buffers,ESD, and bonding pad structures. The 3D-NOR structure may besequentially processed on top of the base structure 108 or a 3D-NORstructure maybe fabricated separately and then bonded into the basestructure later. Multilayer alternating silicon dioxide and highly dopedpolysilicon or alternating silicon dioxide and silicon nitride to belater replaced with metal gate are successively deposited (orepitaxially grown in some cases) forming stack pairs. The common layersare silicon dioxide 103 often called oxide and poly-silicon 105 oftencalled poly. In some common 3D NAND structures, the successivedeposition of silicon nitride (in place of poly-silicon 105) is oftenshortened to nitride. In the 3D NOR-P structures, just as in 3D NANDstructures, the polysilicon 103 could be heavily doped such as n++-typeor p++-type and could be used as the gates for the transistors of whichplane formed by etching holes (often called “punch”) in the multilayerstructure. The holes drawn throughout this invention may be drawncircular; however, the holes are not necessarily circular; rather, forexample, they can be a square, a square with its corners softened(‘champhered’), or ellipsoidal or some combination thereof. The gatesmay also function as the Word-lines (“WL”) of the 3D memory. Herein,these WLs will be drawn along the X direction, which controls one row ofthe arrayed in multiple column channels along the X direction.Alternatively, these WLs will be in the XY plane, which controlsmultiple columns and rows of the arrayed channels in the XY plane. Otherorientations may be possible due to engineering design, process,economics, performance, etc. considerations.

FIG. 1A illustrates a multilayer 106 structure formed over foundationstructure 108 covered with patterned hard-mask 109 after holes 102, 104been etched through. The holes may be punched as an array with ‘columns’along the X direction and ‘rows’ along the Y direction. A single memorycell may consist of three punched holes. The diameter of these holes102, 104 may be the same or different. The holes 102 could be designatedfor the Source/Drain (“S/D”) function and the holes 104 could bedesignated for the nano device Channel function. The space between S/Dhole 102 and Channel hole 104 should be designed small enough so in thefollowing step of indenting the polysilicon 103 layer from the holeside, the polysilicon in-between holes in the X direction would be fullyremoved, as is illustrated in FIG. 28A of PCT/US2018/016759(WO2018144957). The region(s) where S/D hole 102 and Channel hole 104merge is hereinafter referred as the neck region 107. However, the spacebetween rows could be formed to be relatively wide so that the holesalong Y direction are not merged and as the remaining polysilicon layermakes conductive along the X direction it could be used to form theWord-Lines. After such a lateral selective polysilicon etch, the formedneck region may be sharp. A process smoothing the corners of the neckregion such as heat treatment may optionally be added. Within a row theholes could have a relatively narrow gap. The number of pairs in thestack could be below about 10 such as 4 or 8 layers, or below about 100such as 32, 64, or 96 layers, or over about 100 such as 128 or 156layers. Advanced 3D NAND products have now about 128 pairs. The diameterof the holes could be about 10 nm or about 20 nm or about 40 nm or about60 nm or even larger.

FIG. 1B illustrates the structure after selective isotropic polysilicon103 layer etch without removing oxide layer 105, indenting thepolysilicon layers from within the holes, horizontally removing itbetween the S/D holes and the channel holes. While the WL could benarrowed a bit, the WLs in along X direction in between holes in the Ydirection are continuous and their integrity and functionality could bekept.

FIG. 1C illustrates the structure after conformal deposition of a chargestorage layer 111, which may include a combination of blocking oxide,tunneling oxide, and there between a charge trap layer or floating gate.Alternatively, instead of the charge storage layer, a ferroelectriclayer such as HfZrO or HfSiO may be used as a gate dielectric and the 3DNOR structure may be operated according to the ferroelectric randomaccess memory (FRAM) mechanism.

FIG. 1D illustrates the structure after conformal deposition of channelmaterial such as undoped or lightly doped polysilicon, followed by anon-conformal deposition of either the same channel material or other‘dedicated’ material that can seal the hole opening region 110 near thehard mask 109 without contaminating the channel material. For simplicityand clarity, the channel material hereinafter will assume to bepolycrystalline silicon. When the same channel material could be usedfor sealing, as the channel material is being deposited, the channelmaterial can fill the neck region, thereby separating the merged holeinto three respective holes, two S/D holes 102 and one channel 104 hole.When a different ‘dedicated’ material and process is used for sealing, alow step coverage deposition process such as sputtering or non-conformalchemical vapor deposition (CVD) can be used to seal the structure. Tomaximize the non-conformality, a wafer may be tilted during deposition,often referred as glancing angle deposition. The channel material couldalternatively be, for example, polycrystalline silicon-germanium,polysilicon germanium, or amorphous silicon, amorphoussilicon-germanium, amorphous germanium, which could be undoped orlightly doped, for example, not exceeding a doping concentration ofabout 1×10¹⁹/cm³. A process to further crystallize the polysiliconchannel such as laser annealing or alternative annealing step whichavoids excessive dopant diffusion may be added. For example, theblocking oxide thickness could be about 3-10 nm, the charge trap layeror floating gate thickness could be about 3-8 nm, the thin tunnelingoxide thickness could be about 0-5 nm, and the channel polysiliconthickness could be about 5-30 nm.

The exemplary process steps from FIG. 1E to FIG. 1G illustrate theformation of a back-gate for enhancing functionalities, for example,such as, improved retention time, write/erase speed, power efficiency,and disturb immunity. These steps may be skipped if no back-gate isdesired. For example, the portion for the back-gate illustratedhereinafter may remain as a void or may be fully filled with, forexample, a bulk polysilicon channel. FIG. 1E illustrates the structureafter selectively opening the channel holes 112 by etching the sealregion near the hard mask layer 109. During this opening process, theetching should be controlled carefully in order not to damage thechannel material.

FIG. 1F illustrates the structure after filling the back-gate oxide, forexample, such as silicon dioxide and the back-gate, for example, such ashighly doped polysilicon or metal gate, inside the channel holes 112. Ifdesired, the back-gate 114 oxide may be a stack of blocking oxide,tunneling oxide, and there between a charge trap layer or floating gate.Alternatively, the back-gate may be a direct body contact with noback-gate oxide. In this case, the back-gate may be heavily dopedpolysilicon with the same doping type as the transistor channel. Priorto the back-gate process, a process of opening a contact at the bottomof the hole 104 for the back-gate to be linked to the foundationstructure 108 carrying the back-gate control circuits 116 could beincluded.

FIG. 1G illustrates the structure after opening the S/D holes 118, whoseprocess is similar to the process explained with respect to FIG. 1E.

FIG. 1H illustrates the 3D NOR-P intermediate structure after fillingS/D 120 with material. For example, the S/D material could form a pillarof N+ poly, or an N+ polysilicon pillar with a metal core followed byactivation and silicidation, or a full metal pillar. The metal may be atleast one of Ni, Ti, Co, Pt, Al, or other similar Si reactive materials.Or Si non-reactive but conductive, such as W or Ag. In one embodiment ofthis invention, the source and the drain are not symmetric. For example,one of the sources and one of the drains can be metal or metal silicideand the other of the source and the drain are non-metal or non-silicidematerial as illustrated in XY plane view FIG. 1I of FIG. 1H or aslightly modified FIG. 1H. This asymmetric S/D structure maybe desiredfor minimizing ambipolar transfer characteristics, which in some casescould increase the off-state leakage current. Prior to the S/D process,a process opening a contact at the bottom of each of S/D holes 102 forthe S/D to be linked to the foundation structure 108 carrying the S/Dcontrol circuits could be included. Additionally, the processessequences between S/D formation and back-gate formation could beinterchangeable depending on engineering, design, and technology choicesand optimizations.

In another embodiment, one source may be shared with at least twoadjacent channels and drains as illustrated in XY plane view of FIG. 1J.In a further embodiment, the unit pillar cells along the X-direction maybe electrically isolated by isolation oxide as illustrated in FIG. 1K orisolated by chaining source and drains as illustrated in FIG. 1L. Bydoing so, north and south sides of one channel can be independentlycontrolled respectively by north WL and south WL. When the unit pillarcell isolation is conducted in the structure of FIG. 1L, the back-gateplaced in-between adjacent unit pillars may be referred to as an‘isolation back-gate’, which are dedicated to stop inter-pillar leakagecurrent. In one embodiment of the 3D memory chip, a periphery circuitlayer can be placed under or over of the 3D memory array while theinterconnection lines between the periphery and the array can be madeboth to top and bottom of the memory array. In another alternative theperiphery circuits could be on both sides under the 3D array and overthe 3D array.

FIGS. 1M-1Q illustrate an alternative process without dedicated punchholes for the channel pillars, both structure and process flow. FIG. 1Millustrates punch holes for a pair of Source/Drains (S/D) at aseparation distance of narrower space 144 with wider space 142 theseparation distance to the holes of the next pair. FIG. 1N illustratesthe structure after an isotropic polysilicon etch. The isotropicpolysilicon etch is used to create a horizontal indentation of thepolysilicon until the polysilicon of the narrow gap 144 between the S/Dpillars is fully removed but the polysilicon in the wider gap 142between pairs of S/D remains FIG. 1O illustrates the structure afterconformal deposition of a charge trap layer stack (O/N/O) 146 orfloating gate stack throughout the punch holes. FIG. 1P illustrates thestructure after a conformal polysilicon deposition forms polysiliconchannels 148 filling up the narrow gaps 144 in-between the S/D pairs.The holes could be designed to be wide enough so completely filling thenarrow gaps 144 would not completely fill the holes, leaving room for anoptional etch to widen the inner tube of the holes. As illustrated inFIG. 1Q, the S/D holes could be filled with N+ doped polysilicon, ormetal, or combination of N+ doped polysilicon and metal, or theirsilicide as discussed previously for S/D pillars, thus S/D pillars 150may be formed.

According to one embodiment of this invention, a process step for MetalInduced Lateral Crystallization (“MILC”) of polysilicon channel could beapplied in 3D NOR-P process. The MILC process is presented in at least apaper by Lee, Seok-Woon, and Seung-Ki Joo. “Low temperature poly-Sithin-film transistor fabrication by metal-induced lateralcrystallization.” IEEE Electron Device Letters 17.4 (1996): 160-162,incorporated herein by reference. In some literatures, the MILC processis also referred as metal induced recrystallization (MIC) as therecrystallization direction is not always lateral. The similarrecrystallization process is applied in polysilicon channel 3D NANDstructure as presented in U.S. Pat. No. 8,445,347 B2, incorporatedherein by reference. A time required for MIC process in 3D NAND channelusually takes a few hours as the length of the channel is often greaterthan 5 μm. However, a time required for MIC process in 3D NOR-P channelcan be less than one hour as the length of the channel would not beexceeding 0.2 μm. The process step for MIC in 3D NOR-P may be added inbetween the steps related to FIG. 1G and FIG. 1H or between FIG. 1P andFIG. 1Q. When at least one side holes designed for the source or thedrain are opened, a recrystallization metal seed or nucleation promotersuch as nickel, palladium, aluminum, or their combination is conformallydeposited. Then, the recrystallization may be conducted by a subsequentlow temperature annealing ranging from 300 to 600° C. The amorphous orsmall grain polysilicon channel can be converted to a large grainpolysilicon channel or even single crystalline channel. The results ofchannel recrystallization are an increase of carrier mobility, anincrease of the cell current, improvement of cell variability,tightening of the cell threshold voltage distribution, and improvementof retention time. The MILC process could be initiated from just oneside of the channel to reduce the formation of boundaries associatedfrom two crystallization waves meeting if such been initiated from bothsides.

FIG. 2 illustrates a cut view along X/Y and Z 200 direction of a sectionof a 3D NOR-P structure. This embodiment offers periphery sandwiching onboth sides, under as well as over, the 3D memory array structure. In oneexample, the periphery under the cell memory control circuits 246 maycontrol S/D and WLs while the periphery over the cell 250 may controlback-gates, or vice versa, or a shared combination. A 3D NOR-P structuremay include a base wafer 242, an optional ‘cut-layer’ 244, memorycontrol circuits 246 disposed under the 3D NOR memory array 248, andoverlaying control circuit 250. Memory control circuits 246 could beused to control the back-gate while overlaying control circuit 250 couldbe used to control the S/D pillars.

The formation of a multi-level 3D structure could utilize any of thetechniques presented in the incorporated art such as at leastPCT/US2017/052359, incorporated herein by reference, such as had beenpresented in reference to its FIGS. 11F-11K, FIGS. 12F-12J, or FIG. 21Ato FIG. 25J. Some of levels could be integrated using Hybrid Bonding andsome could be integrated using other type of bonding followed by formingthe connectivity.

FIGS. 3A-3B are two exemplary circuit schematic illustrations of asection of the Back-Gate control circuit which may reside in foundationstructure 108 along the X-Y 300 direction.

FIG. 3A illustrates a control per column circuit (along Y direction) infoundation structure 108 for back-bias pillars 308 of a 3D memory array.A control line, Ci or Column ‘i’ Select 302 allows switching a column ofBack-Bias pillar or back-gate voltage (Vbg) being fed by between Holdingvoltage 304 using transistors 312, to access back-bias voltage 306 usingtransistors 310. The holding voltage is designed for extending the dataretention time of the memory during standby. The holding voltage will bechosen depending on the characteristics of the memory cell. For example,when the loss of electrons in the charge trap layer of a programmed cellis due to disturb conditions or standby is stronger than the accidentalinjection of electrons to the charge trap layer of the erased cell, thenegative holding voltage to the back-gate may suppress the electron lossbecause the electric field pushes the electrons toward the WL.Inversely, if the accidental charge injection to the charge trap layerof an erased cell is due to disturb conditions or standby is strongerthan the loss of electrons in the written state, a positive holdingvoltage to the back-gate may be used. In addition, the back-gate columnin which a cell is being accessed will have the back-bias voltage Vbgaccording to the design read or write back-bias voltage. A positiveback-gate voltage may be used to remove the stored elections or erasethe cell. A positive back-gate voltage but the same or smaller than thepositive back-gate voltage used for the erase may be used to read thecell, which amplifies the read current and reduces the read time by adouble-gating manner. A negative back-gate voltage may be used to pushthe electrons to be stored or program the cell. A negative back-gatevoltage but the same or smaller than the negative back-gate voltage usedfor the programming may be used to bias all the other unselected cells,which suppresses the overall leakage current.

FIG. 3B illustrates an alternative control per column circuit infoundation structure 108 with an additional transistor 314 which allowsan additional per-row control 321, 322, 323 for the selected column. Thecells other than the selected row would have their back-bias floatedwhile the one cell of the selected row (Rj Select active) would be apotential Vbg. Such an additional per row selection could help reducethe probability for read/write disturb (reading or writing of anunselected cell).

FIG. 4A is an alternative configuration to FIG. 13A of PCT/US2018/052332(WO 2019/060798). It illustrates an X-Y 400 cut of a 3D NOR-P structure.The Word-Lines (WL1, WL2 . . . ) between rows of memory cells areoriented in the X direction. WLs from WL1 to WL8 are one body at theedge of the 3D unit block so that they supposed to receive a commonwordline voltage. Each Word-Line (WL1-WL8) has respective per row WLselect transistors RS1-RS8 (also called ridge-select) so that onlyselected WL through a selected RS transistor receives the wordlinecontrol voltage while remainder of the unselected WLs are floating.Optionally, on the other side a complementary structure could provide a(‘weak’) pull down pillar connection 402 for the unselected word-lines.At each level the word-lines have a common Y connection strip 404 toallow a Y oriented stair-case for the per-level contacts.

FIG. 4B illustrates an alternative control per column circuit in theoverlaying periphery structure 250. The circuit illustration is alignedin an X-Y 400 view per one column i having an activated decoded 401column control signal Ci. There may be two global control signals;Source signal 410 and Drain signal 412. For the activated column I oneof these signals will be transferred to the left side S/D contact (430,432, 434, . . . ) and the other will be connected to right side S/Dcontact (431, 433, 435, . . . ). The choice which side receives theSource 410 signal and which the Drain 412 signal is control by the logicsignal S/D and its inversion S/DB using the selector circuit of the fourtransistors 414, 415, 416, 417. And for a Ci signal this selection wouldbe wired through the enabling transistors 407, 408 to the two relevantS/D columns A row selection signal Rj Select (421, 422, 423, . . . )could be used to enable these signals to the specific selected row S/Dpillars through a vertical transistor (not shown) at the top of the S/Dpillars.

Embodiments of the present invention are a 3D NOR-P device and its arraythat sense data using voltage sensing process with a voltage senseamplifier. The voltage sensing process determines the stored memorystate by pre-charging a same voltage into a selected bit line to be readand a reference bit line coupled to a reference. The reference bit linemay be a fixed voltage supplied from a periphery circuit or thereference bit line may be bit line different from a selected bit line,namely an unselected bit line. The pre-charged voltage levels on theselected bit line and reference bit line asymmetrically shifts byflowing a different level of current through to the selected bit lineand reference bit line depending on the threshold voltage of theprogrammed or erased state of the selected memory cell. The developedpotential difference between the selected bit line and reference bitline is then sensed by a coupled voltage sense amplifier. When theselected cell is at the erased state or low threshold voltage state, adrive current flows through the source line and bit line of the memorycell and thus the selected voltage falls fast relative to that of thereference cell. When the selected cell is at programmed state or highthreshold voltage state, a subthreshold leakage level current or nocurrent flows through the source line and bit line of the memory celland thus the selected voltage falls slowly or is stable relative to thatof the reference cell. These allow a fast differential voltage senseamplifier to sense data and verify operation.

In one embodiment, the reference bit line can be a bit line in a pairedunit or mat or bank that is associated with the unit or mat or bankbeing accessed. Or the reference bit line can be a bit line reserved anddedicated as the reference cells where all memory cells associated withthe reference bit line are at high threshold voltage.

In a charge trapped memory transistor formed, as an example, with an n+doped source and n+ doped drain, Fowler-Nordheim (FN) tunneling isinherently slow for DRAM replacement or even storage class applications.For example, the write speed using FN tunneling is greater than an orderof few microseconds. On the other hand, the writing speed using hotcarrier can offer faster speed, shorter than a microsecond, which isfaster than FN tunneling. Nevertheless, the write speed near amicrosecond is not applicable for DRAM applications. In order togenerate hot electrons in the charge trapping memory using n+ dopedsource and n+ doped drain, the source is grounded and a high positivevoltage is applied to the drain and the gate. At this condition, theelectrons injected from the source are accelerated and become energeticnear the drain junction. The majority of the electrons are swept intothe drain and a fraction of the electrons, such as less than 1% of thedrain current, is captured in the charge trapping site. The sameacceleration mechanism with reverse voltage polarity applies to thehot-hole generation for an erasing operation. The hot-carrier mechanismconsumes a high power for the programming and erasing, which limits thetotal number of bits that can be simultaneously written in parallel. Inaddition, a fundamental drawback of the charge trapping memory using n+doped source and n+ doped drain arises in 3D memory which commonly usesa polysilicon channel for the memory cell transistor. In order for theelectrons or holes to become hot or energetic, the carries needs to beaccelerated, yet any scattering events retard the acceleration. As aresult, whereas the hot carrier generation is feasible in a singlecrystalline silicon channel, the same does not occur in conventionalpolycrystalline silicon channel, because the electrons and holesexperience phonon scattering and grain boundary scattering inpolysilicon channels; for example, such as is presented in a paper byLiu, Po-Tsun, C. S. Huang, and C. W. Chen. “Nonvolatile low-temperaturepolycrystalline silicon thin-film-transistor memory devices withoxide-nitride-oxide stacks.” Applied physics letters 90.18 (2007).Therefore, the lucky electron injection model is usually not applicablefor a polysilicon channel. As the channel of 3D charge trapping memory,also been referred to as 3D NOR-P in this invention, is formed bychemical vapor deposition (CVD), the channel tends to bepolycrystalline. As a result, the hot-carrier generation in 3D chargetrapping memory could be very difficult.

In order to solve the challenge associated with a polysilicon channel ofhot-carrier generation in the 3D charge trapping memory, also beenreferred to as 3D NOR-P, presented in this invention and in theincorporated by reference patents and applications, a metal source andmetal drain is presented, also been referenced to forming a Schottkybarrier between Source or Drain and the channel. Unlike the conventionalneeds for the carrier to be accelerated traveling through channel fromsource for hot-carrier generation, for sources formed by metal-singlecrystalline silicon channel as well as metal-polycrystalline siliconchannel, forms abrupt energy band banding in the Schottky junction.Thus, the carrier could be accelerated without the need to travel thechannel. As a result, the hot-carrier is generated near the source sidein a Schottky junction unlike the common case of single crystal pnjunction in which the hot carriers are generated near the drain. Suchmechanisms are discussed in many of the art presented in the relatedapplications and patents incorporated by reference in here such as inpapers by Shih, Chun-Hsing, et al. “Schottky barrier silicon nanowireSONOS memory with ultralow programming and erasing voltages.” IEEEElectron Device Letters 32.11 (2011): by Shih, Chun-Hsing, et al.,“Schottky barrier silicon nanowire SONOS memory with ultralowprogramming and erasing voltages.” IEEE Electron Device Letters 32.11(2011): 1477-1479; by Ho, Ching-Yuan, Yaw-Jen Chang, and Y. L. Chiou.“Enhancement of programming speed on gate-all-around poly-siliconnanowire nonvolatile memory using self-aligned NiSi Schottky barriersource/drain.” Journal of Applied Physics 114.5 (2013): 054503; and byChang, Wei, et al., “A localized two-bit/cell nanowire SONOS memoryusing Schottky barrier source-side injected programming.” IEEETransactions on Nanotechnology 12.5 (2013): 760-765, all of theforegoing in their entireties are incorporated by reference herein.

In addition to the hot-carrier generation in polysilicon channel, thereis also important advantages in Schottky-junction based charge trappingmemory (3D NOR-P). As explained earlier, in conventional channel hotcarrier injection, different voltages need to be applied to the sourceand drain in order to create a flow of current through the channel andaccelerate the carriers. Only a very small fraction of carriers arebeing used for the charge storage, thus wasting more than 90% of thepower. In the charge trapping memory using Schottky barrier, the samevoltage can be applied to the source and the drain so that no currentflows across the source and the drain. Rather, the injected current fromany or both sides of the source or drain tends to be captured in thechange trapping layer because the electrical potential is formed for thecarrier favorable to move toward the gate or wordline. This fact impliesthe writing and erasing can not only be fast but also consumes a muchsmaller writing power compared to the conventional pn junction. In fact,not only the conventional charge trapping memory using hot-carrierprogramming but also many of emerging memories such as MRAM, RRAM, andPRAM are constrained in parallel writing due to high write power.Therefore, such a constraint limits their use for wide bus widthapplication, limiting massive parallelism. The Schottky junction chargetrapping 3D memory (3D NOR-P) presented here and in the relatedapplications and patents incorporated by reference herein could consumeorders of magnitude lower write power, thus enabling wide bus widthapplications. The page size represents essentially the number of bitsper row. The page size is the number of bits loaded into or written backfrom the sense amplifier when a row is activated. The page size of theSchottky junction charge trapping 3D memory (3D NOR-P) can be greaterthan 2 KB or 4 KB, or even greater than 16 KB. When the wide page sizeapplication is enabled, the clock frequency or timing parameters such asRow Address to Column Address Delay and Column Access Strobe—“CAS”latency can be relaxed, which can further reduce the power consumption.The wide bus width with relaxed timing parameter is particularlybeneficial for mobile applications such as, for example, smartphones ortablets.

A 3D NOR-P memory using a Schottky junction and polycrystalline channeloperation scheme is shown in FIG. 5A-5C. The dotted line in the FIG. 5Arepresent the energy band diagram for WL=BL=SL=0V. As is illustrated inFIG. 5A, for write ‘1’, −1.5 V is applied to WL and 1.5 V is applied toSL/BL. The hot holes are injected from the Schottky junction and trappedinto the charge trapping layer. In some cases, particularly wherein theFermi level of the metal is pinned close to the conduction band ofsilicon, the trapped electrons are detrapped by FN tunneling. Thetrapped holes or removal of the trapped electrons decrease the thresholdvoltage. For a write ‘0’, 1.5 V is applied to the WL and −1.5 V isapplied to the SL/BL. The hot electrons are injected from the Schottkyjunction and trapped into the charge trapping layer. The trappedelectrons increase the threshold voltage. In order to use WL=0V for theshut-off voltage to unselected rows, the target threshold voltage ofstate ‘1’ is slightly greater, but not limited to, than 0V such as0.2V˜0.4V. For the unselected device, WL/SL/BL are grounded. For thehalf-selected cells, the voltage difference from WL to SL or WL to BL is1.5 V, which could be a condition to be too small for Schottky junctiontunneling. Therefore, the programming could be inhibited. As isillustrated in FIG. 5B-C, for read, the WL voltage of 1 V is applied sothat the current difference due to threshold voltage difference can besensed. The unselected WL is grounded so that minimal BL current flowsregardless of the memory states. In order to use WL=1V for the readvoltage to the selected row, the threshold voltage of the state ‘0’would be slightly greater, but not limited to, than 1 V such as1.2V˜1.4V.

As presented in the incorporated by reference art and related patentsand application, alternative writing schemes could also be used.Different writing condition for 3D NOR-P type memory having SchottkyBarrier is used to drive current through the channel to program or eraseonly close to the source-side or drain-side or both sides of Schottkyjunction. This allows two memory zones per channel, one near the sourceand another near the drain, as also known as a mirror-bit scheme. Suchhas been presented in reference to FIG. 17, FIG. 19, FIG. 21 and FIG. 23of U.S. Pat. No. 10,014,318, incorporated by reference, and FIG. 13A-13Dof patent application Ser. No. 16/337,665 (published as US2019/0244933), incorporated by reference in its entirety. In some of thepatents or applications incorporated by reference the reference to such3D memory included similar terms to, such as, 3D charge trapping memory,3D NOR, 3D NOR-P, 3D NOR-C. The unique advantages relating to the use ofa metalized Source having a Schottky Barrier is relevant to all of thesestructure and perhaps far more so, for those techniques and structuresutilize a polysilicon channel. The mirror-bit operation scheme in the 3DNOR-P memory using Schottky junctions and a polycrystalline channeloperation scheme is shown in FIG. 5D-5E. The dotted line in the FIG. 5Drepresents the energy band diagram for WL=BL=SL=0V. As is illustrated inFIG. 5D, for write ‘1’ into the source side, −1.5 V is applied to theWL, 1.5 V is applied to the SL, and 0V is applied to the BL (drainside). The hot holes are injected from only the source side's Schottkyjunction and are trapped into the charge trapping layer near the sourcewhereas no significant hole injection takes place in the drain side'sSchottky junction. Similarly, for write ‘1’ into the drain side, −1.5 Vis applied to the WL, 0 V is applied to the SL, and 1.5 V is applied tothe BL (DL). The hot holes are injected from only the drain side'sSchottky junction and trapped into the charge trapping layer near thedrain whereas no significant hole injection takes place in the sourceside's Schottky junction. For write ‘0’ into the source side, 1.5 V isapplied to the WL, −1.5 V is applied to the SL, and 0V is applied to theBL (DL). The hot electrons are injected from only the source side'sSchottky junction, whereas no significant electron injection takes placein the drain side's Schottky junction. Similarly, for write ‘0’ into thedrain side, 1.5 V is applied to the WL, 0 V is applied to the SL, and−1.5 V is applied to the BL (DL). The hot electrons are injected fromonly the drain side's Schottky junction, whereas no electron injectiontakes place in the source side's Schottky junction. When the write ‘0’or write ‘1’ operation is made on one side of junction, the memory stateof the opposite side does not affect its writing operation. In order toreduce disturb the memory state of one side against another side, thechannel length of the memory transistor could be made greater than 100nm. In this case, particularly the Fermi level of the metal is pinnedclose to the conduction band of silicon, the trapped electrons aredetrapped by FN tunneling instead of hot hole injection. In this case,the block erase rather than bit-specific erase would be favored.

FIG. 5E illustrates the read operation for a source side read. In orderto read the source side's memory state, the SL is grounded and a readvoltage is applied to the BL (DL) and vice versa. The drain side read isnot drawn but it is the reciprocal by swapping SL and BL (DL) voltages.For read, a voltage such as 1V is applied to the WL for both a sourceside as well as a drain side read. Other but different voltages areapplied to the SL and BL (DL), and the current is measured to detect thethreshold voltage associated with the charge trapping element. Forexample, SL=0V and BL=1V (DL=1V) is applied to sense the source side'sstorage state and SL=1V and BL=0V (DL=0V) is applied to sense the drainside's storage state. The threshold voltage is dominated by the chargetrapped state near the ground node and the charge trapped states (‘0’ or‘1’) near the read voltage biased node is masked as illustrated inenergy band diagram in FIG. 5E.

It should be noted that the use of 1V, 1.5V, −1.5V in FIG. 5A-5E and therelated description are just an examples and the specific voltages usein specific devices are highly related to the specific device structureand could be varied accordingly. An example of other operating voltagesfor Schottky Barrier based charge trap devices with polysilicon channelis presented in at least a paper by Chang, Wei, et al., “Drain-inducedSchottky barrier source-side hot carriers and its application to programlocal bits of nanowire charge-trapping memories.” Japanese Journal ofApplied Physics 53.9 (2014): 094001, incorporated herein by reference inits entirety, illustrating these two writing modes in respect to itsFIG. 4. While there could be many design considerations choosing devicestructure, operating method, and voltages, there is one aspect relatingto the relatively low programming voltages presented in reference toFIGS. 5A-5E. A relatively low programming voltage could be used to forma relatively low threshold voltage shift, such as 1 volt, which couldhelp overcome the ambipolarity of some Schottky barrier based devices.Such was presented also in PCT/US2018/016759, incorporated herein byreference, in reference to at least its FIG. 12A-12D.

Furthermore, in some devices the memory control circuits, such as 250and 246, could include additional circuits such as controllers andsensors such as temperature sensors to support modifying these biasvoltages. Such on the fly environmentally driven signal levelmodifications are common in memory devices and could be designed/adaptedto compensate for various issues, including short time adaption and longterm adaption. Such control could be used for many of the deviceoperations including also changing the rate of refresh and otheroperation such as relate to at least FIGS. 6A-6G herein.

FIG. 6A illustrates a transfer curve or drain current versus gatevoltage characteristic of a charge trap memory cell. The thresholdvoltage transfer curve of the as-fabricated device 602 is determined bythe native trap states. For the as-fabricated states, the thresholdvoltage is usually lower because the traps are mostly empty. Each trapthat is capable of storing an electron has its own location and energystate. Some traps are located far from the channel and close to theblocking oxide but other traps are located far from the blocking oxideand close to the channel. Apart from its physical location, some trapshave deep energy states but other traps have shallow energy states.Depending on its location and energy depth, the voltage and timerequired to store and remove electrons to these traps varies. Forexample, a higher voltage and/or longer pulse width may be required tofill/empty the traps close to the blocking oxide and the traps with deepenergy states. However, a lower voltage and/or shorter pulse width maybe required to fill/empty the traps close to the channel interface andthe traps with shallow energy states. In this case, the deep energystate trap is often called a slow trap while the shallow energy statetrap is often called a fast trap. During the formation of the chargetrap layer, trap energy distribution is very random so it is almostimpossible to exclusively fabricate a device with just fast traps.Accordingly an operational method could be adapted to nullify the effectof the slow traps. The method is illustrated as a flow chart in FIG. 6B.First, the charges traps with all energy states are fully saturatedbefore normal operations such as read, write, hold, and refresh. Thisoperation may be called the preset mode. The preset operation can beaccomplished without a memory controller. For example, when the systempower is turned on, the memory internal periphery circuit can conductthe preset operation during the calibration period. Alternatively, thepreset operation can be conducted by order of memory controller. Thepreset can be conducted only once for its first use. Alternatively, thepreset can be respectively conducted as for its functional maintenance.The preset mode would be similar to the program operation of the memorybut with a higher word-line voltage and/or longer program pulse width.The preset mode is activated as initiation process 612 such as when thememory is booted. Then, during normal operation 614, the devicecontroller uses write and erase voltages that are limited so not todisturb or remove those trapped electrons in the deep energy states. Asa result, the transfer curve for the programmed state 606 would besimilar to the transfer curve after the preset operation. For the erasedstate, the threshold voltage is lowered but not fully lowered 604. Theamount of the threshold voltage shift (“Vt”) therefore between theprogrammed state 606 and erased state 604 is determined by the amount ofthe shallow trap density. By nullifying the involvement of the deeptraps, the charge trap memory may work at a higher speed. Assuming thatthe Vt for the cell with fully emptied charge trapped state is Vt,minand the Vt for the cell with saturated filled charge trapped state isVt,max, only part of Vt window is used in this method of memoryoperation. The maximum capable Vt window is ΔVt,max=Vt,max-Vt,min, Vt ofmemory state ‘0’/programmed state could be similar to Vt,max but Vt ofmemory state ‘1’/erase state could be Vt,max-αΔVt,max, where α could be0.05, 0.1 or 0.2. In other words, the programmed cell (‘0’) could be ina fully filled charge state and the erased state (‘1’) could be apartially emptied charge state which may be achieved by preferentiallyeliminating shallow trap level electrons. If required 616, the thresholdvoltage shift from the fully saturated state or programmed state couldbe monitored, and a preset mode could be intermittently triggered. Sucha partial erase could be achieved by shortening the time of the eraseoperation by 50% or 80% or even more than 90%. So, for example, if for aspecific memory structure the erase and full removal of the chargetrapped could take more than a microsecond (μs), the partial erase couldbe performed in less than 0.5 μs or less than 0.1 μs or even less than30 ns.

The concept presented with respect to FIGS. 6A-6B could also be used toimprove other types of memory such as Ferroelectric (“FE”) memories.Ferroelectric memory such as presented in respect to FIG. 24A-FIG. 26Hof PCT/US2018/016759, incorporated herein by reference, are attractiveas a high speed memory but considered to have a limited endurance ofabout 10⁶. An undesired charge trapping at the gate stack is asignificant factor in the limiting of the memory endurance. The conceptof shifting the memory threshold could help in nullifying the effect ofthis undesired charge trapping. This charge trapping is a very slowprocess and once charge has been trapped it will stay trapped for longtime. Accordingly the memory block could be tested by the memorycontroller and the memory threshold could then be adjusted.

This concept could be further illustrated in respect to FIGS. 6C-6E.FIG. 6C illustrates charge trapping operation, i.e., threshold voltageshift for the charge traps from the empty state to an electron saturatedstate. As programming time increases, the threshold (Vt) shift grows asmore electrons get trapped. Early on, the low energy trapping locationsget filled up first and then the higher energy trapping locations arealso filled up with electrons as the programming operation continues.Therefore, the programming rate is high in the early stages and theprogramming rate becomes lower as the trapping sites become saturated. Akey aspect is a charge trapping structure that could be at a fullysaturated threshold voltage within a reasonable Vt distribution. Suchcould be achieved by limiting the charge trapping layer volume bylimiting the charge trapping layer thickness and developing a uniformquality nitride layer process having uniform trap density and trapenergy distribution across chip area. Accordingly, the 3D memory couldbe structure with charge trapping layer thickness of less than 2 nm or 3nm or 5 nm or 7 nm. The charge trap layer trapping capacity is highlydependent on its volume/thickness and the level of trapping sites in itwhich depend on layer material composition and formation process.Furthermore, the film integrity of the blocking oxide could be densehaving inherently minimal trap density. The inverse would happen duringan erase operation as is presented in FIG. 6D. Early on the low energytrapping sites get erased which is indicated by the fast reduction ofthe Vt shift because the charges trapped in the shallow level arefavorably removed than those in the deep level. Then as the eraseoperation continues the electrons at the high energy trapping sites alsoget moved out, and if the erase operation continues some holes gettrapped resulting in an “over-erased” state. In general, the programmingrate is higher than the erasing rate. In order to obtain a balancebetween the program speed and the erase speed, the memory statethreshold voltage window is partially utilized by maximizing the erasespeed but compromising the programming speed as illustrated in FIG. 6E.First, the initialization process is necessary to fully saturate thethreshold voltage shift by storing electrons in the charge trappingsites. This process may take long enough such that substantially all ofthe trap sites get programmed with electrons. Then the normal programand erase operation can follow. For the programmed state, the chargetraps are fully filled with electrons. For the erased state, only chargetraps with low trapping energies are selectively removed. The pulsewidth for the programming and erasing may be set to be the same. Theprogramming pulse width is set to saturate the charge traps.

There might be the die to die or wafer to wafer variability in terms ofits saturation Vt. In order to address those variability, the memoryperipheral circuit may include built-in self-test (BIST). The BIST teststhe program and erase voltage to meet a required programming and erasingtiming parameters and reflect them into a programmable structure such asprogrammable resistors, anti-fuses, etc. Accordingly, a slightlydifferent program, read, erase voltages could be used per every memorysub-array basis or memory bank basis. In addition, if the BIST resultsshows that some cells do not meet the required timing parameters, thememory structure could include redundancy so WL which include defectivecells could be disabled and replaced with a WL for the redundant cells.Such a test is often called post-package-repair (PPR). In addition, theenergy level and density of trapping sites could also change over timeand accordingly over time the method suggested herein in respect to FIG.6A-6D could include periodic adjustments to track device changes overtime. Such could be at relatively high rate of hours in someapplications, days in other applications or even months.

An additional benefit from the techniques presented here in reference toFIG. 6A-6E, called “Pre-Charging,” relates to the memory retention time.FIG. 6F illustrates a conventional flash memory retention time chartthat uses fully filled charge traps and fully emptied charge traps. Thecharge of the programmed cells is leaking out causing the thresholdvoltage associated with programmed cells V_(T0) to move down, while theerased cell accumulates charge and their respective threshold voltage ismoving V_(T1) up, closing the memory window from both sides. Therefore,the reference voltage is set to very middle of V_(TO) and V_(T1). FIG.6G illustrates the retention characteristics time chart for flash cellsusing Pre-Charging. It illustrates that, in this case, the thresholdvoltage for both V_(T0) as well as V_(T1) are moving down over time,because the data retention mechanism is electrons leaking for bothprogrammed and erased states. Therefore, the reference voltage can beset to between V_(T0) and V_(T1) but much closed to V_(T1). Accordingly,the Pre-Charging technique helps by extending retention time.

Such leakage is also a drawback, which could be overcome by the devicecontroller periodically performing a self-test and ‘refreshing’ thepre-charging. Such a maintenance mode could utilize the idle time of thememory to avoid interfering with the device normal operation.

FIG. 7A illustrates an advantage for use of metallic bit lines (S/D). Ingeneral, the metal has a good thermal conductivity in comparison to allthe other materials present in such a device. Therefore, these metallicpillars could help remove the heat from the inside of the 3D memorystructure to the top or the bottom surface of the memory structure. Theheat could be then conducted out to the device top surface or bottomsurface. The device cooling then could affect the entire memorystructure. It should be noted that conducting out the heat could be donewithout forming any leakage between these pillars. Such heat conductivetechniques which do not form an electrically conductive path are knownto artisans in the art and presented in some of the art incorporatedherein by reference in the cases discussing heat removal; for example,at least U.S. Pat. Nos. 9,023,688 and 9,385,058.

FIG. 7B illustrates a portion of the device with top silicon substrate714, and bottom silicon substrate 716. The device could comprise athermal path, not shown, from the S/D pillars to these substrates 714,716 without forming electrical path using techniques such as beenpresented in the incorporated by reference art. Landing pads 720 couldinclude those types of structures which conduct heat but notelectricity. The substrates could have good heat conduction. And fromthe substrate, the heat could be removed using techniques well known inthe semiconductor industry.

The heat mobility through the metalized source or drain pillars asillustrated in FIG. 7A, could also be utilized in the other direction tobring heat into the channel to help initiate channel recrystallizationas has been detailed herein with respect to Metal Induced LateralCrystallization (“MILC”) of the polysilicon channel.

The 3D NOR-P as presented herein could be used for high capacity DRAMapplications. Artificial Intelligent (“Al”) using Deep Neural Networks(“DNN”) are becoming the driver of electronics systems and accordingly agrowing part of the DRAM devices are use for these application. In suchsystems the majority of the memory access is for reads and less than 30%of the memory access is from writes. Such use cases work well with the3D NOR-P technology presented herein. Yet while for conventional DRAM agroup of memory bits could be accessed in parallel by having all of themcontrolled with the same wordline for read and for write, for 3D NOR-Pthe wordline voltage for write ‘1’ (programming) is very different thanfor write ‘0’ (erase). Accordingly the memory control needs to bedifferent than in a DRAM. 3D NOR-P memory control could use two cycles;one for the bits that are to be programmed and one for the bits thatneed to be erased. Another alternative is to leverage the finegranularity of the 3D memory structure illustrated in FIG. 2 herein andFIG. 6 of PCT/US2018/52332. Accordingly the parallel access could bemade to bits that do not share the same wordline. In such an accessscheme, the memory control circuits could set the proper conditionsindependently to each of the memory cells being accessed. An artisan inthe memory art can designed the detailed circuit for such a memory.

FIG. 8 illustrates various options for reading a 3D NOR-P device orstructure. Option 1 utilizes the differential mode memory scheme. Inorder to store one bit, two physical memory transistors are used whereincomplementary bits are in each memory cell. One memory pillar structurehas a complementary memory pillar structure that stores thecomplementary data. The memory pillar and complimentary memory pillarmay be located within the same or different memory tiles or blocks. Thesame WL voltage for read is applied to both the selected WL and thecomplementary WL. The read operation can be accomplished by using avoltage latch sense amplifier, similar to the sensing for the doubleended SRAM.

Option 2 utilizes memory transistors in a fixed layer in a pillar asdedicated reference transistors. The threshold voltages of the referencememory transistors are managed and maintained to the reference thresholdvoltage explained in FIG. 6G. The memory pillar for the reading and thereference pillar are located at different memory tiles or blocks.Therefore, only the WL voltage for read is applied to the selected WLlayer but no WL voltage is applied to the same level of the referencepillar. During read, the reference WL voltage is applied to thereference WL layer of the reference pillar. The read operation can beaccomplished by using a voltage latch sense amplifier, similar to thesensing for the double ended SRAM.

In option 3, the reference voltage may be synthesized by using CMOSlogic transistors and used as a reference voltage. The read operationcan be accomplished by using a voltage latch sense amplifier, similar tothe sensing for the double ended SRAM.

In option 4, a current sensing method may be used to read, which usesthe difference in current level for the difference in memory state. Thecurrent amplifier magnifies the level of the current, where thedifferent current results in different voltage rising time. The trippoint detect circuit senses the timing tacked for the output voltage toreach a certain level.

FIG. 9A illustrates a 3D NOR-P option having control logic circuitry,which is often called periphery under cell or cell over periphery. TheS/D lines could be called bit lines or sometimes the Source lines couldbe called select-lines (SL) and the Drain-lines could be called bitlines. The planes such as WL layers are crossing multiple pillars. Asense amplifier is placed underneath every pillar and dedicated for eachrespective BL pillar.

FIG. 9B illustrates the fine-grained memory tile or block. One memorytile or block includes two BL pillars sharing a common global BL. Theone BL pillar out of two BL pillars in the same memory block can beselected by using a two to one multiplexor. Alternatively, for largergrained memory tiles or blocks having n BL pillars sharing a commonglobal BL, one out of n BL pillars can be selected by using an n-to-1multiplexor. Then, the selected BL signal is connected to the globalsense amplifier or row buffer. Alternatively, a local sense amplifier isplaced underneath every fine-grained memory tile and dedicated forrespective memory tiles (not drawn), and then fed into the global rowbuffer.

FIG. 9C illustrates the use of only global sense amplifiers by selectingonly one out of many BLs. In this case, the BL capacitance issignificantly reduced, thereby improving latency timing parameters.

One disadvantage of a 3D NOR-P device having an ultra-thin (less than0.5 nm) tunneling oxide for DRAM applications is the extra energyassociated with the memory refresh operation. Yet in most systems, thememory used is relatively large and could include multiple devices. Insuch systems most of the memory is in a hold state while only one deviceand only one section within the device is been accessed. An optionaltechnique which could help reduce the need for refresh is a “Hold” statefor the device or for device sections. In such a “Hold” state all thewordlines of the device or the section of the device being held in Holdstate could be pulled high to a Hold voltage such as about 0.5 volt orabout 1 volt or even higher than 1.5 volts. Such a Hold voltage for thewordlines could help keep the trapped charge trapped yet it is lowenough not to cause more charge to be trapped. Such a Holding voltagecould be removed and replaced with the normal operating voltage(s) oncethe device or the section being accessed or get other forms ofinstruction to get out of Hold state into normal operating state. Suchholding voltage could be designed as active or passive (via diode) tonodes 402 of FIG. 4A or included as part of the memory control circuits.An artisan in the memory art can design the detailed circuit for such animproved memory control. This technique is also useful for mitigatingmemory cell Vt drift due de-trapping and leakage caused by totalionizing dose effects, for example, such as from gamma rays, forradiation hardening objectives.

An alternative concept could also be used to nullify the effect of thisundesired charge trapping. This could allow managing the cases in whichthe undesired charge trapping is varying between different cells in thememory block. In such cases the read process could be replace with:1^(st) Read, Write ‘One’, 2^(nd) Read and measure difference A betweenthe results of 1^(st) Read, vs. the 2^(nd) Read. A cell that was ‘One’the difference A would be smaller than a set threshold while a cell thatwas ‘Zero’ the difference A would be higher than the set threshold. Sucha self-differential read cycle would need a final step of re-writing‘Zero’ for the ‘Zero’ cells.

An additional alternative for high speed memory using the 3D NOR-Pstructure is the use of the FB-RAM concept as presented in reference toFIG. 29A-29D of PCT/US2018/016759, incorporated herein by reference. TheFB-RAM could have a back-bias for keeping the charge in the floatingbody or to use a re-fresh such as the Auto-Refresh technique presentedin respect to FIG. 86-FIG. 88 of U.S. Pat. No. 10,014,318, incorporatedherein by reference. Such 3D NOR-P structure could use Source and orDrain pillars which have N+ type polysilicon at the outer ring and acore of metal; or even use the technology of Dopant Segregated SchottkyBarrier (“DSSB”) for at least the memory transistors.

The multi-level 3D structure could utilize a hybrid of memory types, forexample, such as one with an ultra-thin tunneling oxide and others withthick tunneling oxide, as presented in the incorporated art such ofPCT/US2016/52726, incorporated herein by reference, such as had beenpresented in sections [00121] to [00132] and such as in reference to itsFIG. 16A-FIG. 17. These memory variations could be processed within thesame 3D memory device allowing lower power transfer of data between thehigh speed cells to the long retention cells and other advantages.

It will also be appreciated by persons of ordinary skill in the art thatthe invention is not limited to what has been particularly shown anddescribed hereinabove. For example, the use of SiGe as the designatedsacrificial layer or etch stop layer could be replaced by compatiblematerial or combination of other material including additive materialsto SiGe like carbon or various doping materials such as boron or othervariations. And for example, drawings or illustrations may not show n orp wells for clarity in illustration. Furthermore, any transferred layeror donor substrate or wafer preparation illustrated or discussed hereinmay include one or more undoped regions or layers of semiconductormaterial. Moreover, transferred layer or layers may have regions of STIor other transistor elements within it or on it when transferred.Rather, the scope of the invention includes combinations andsub-combinations of the various features described hereinabove as wellas modifications and variations which would occur to such skilledpersons upon reading the foregoing description. Thus, the invention isto be limited only by appended claims

We claim:
 1. A 3D memory device, the device comprising: a plurality ofmemory cells, wherein each memory cell of said plurality of memory cellscomprises at least one memory transistor, wherein each of said at leastone memory transistor comprises a source, a drain, and a channel; and aplurality of bit-line pillars, wherein each bit-line pillar of saidplurality of bit-line pillars is directly connected to a plurality ofsaid source or said drain, wherein said bit-line pillars are verticallyoriented, wherein said channel is horizontally oriented, and whereinsaid channel is isolated from another channel disposed directly abovesaid channel.
 2. The device according to claim 1, wherein each memorycell of said plurality of memory cells comprises a charge trap memory,wherein said channel comprises polysilicon, wherein said source and/orsaid drain comprises metal atoms, and wherein said metal atoms enablehot electron programming of said charge trap memory.
 3. The deviceaccording to claim 1, wherein said channel comprises a circular shape oran ellipsoidal shape.
 4. The device according to claim 1, wherein saidplurality of memory cells comprise a partially or fully metalizedsource, and/or a partially or fully metalized drain.
 5. The deviceaccording to claim 1, wherein said plurality of memory cells comprise atunneling oxide thinner than 1 nm.
 6. The device according to claim 1,wherein said channel comprises crystallized polysilicon, wherein saidcrystallized polysilicon was crystallized from heat originating fromsaid source or said drain of said channel, and wherein said channelcomprises at least one crystallization front which originated in eithersaid source or said drain of said channel.
 7. The device according toclaim 1, wherein said at least one memory transistor is self-aligned toan overlaying another said at least one memory transistor, both beingprocessed following the same lithography step.
 8. A 3D memory device,the device comprising: a plurality of memory cells, wherein each memorycell of said plurality of memory cells comprises at least one memorytransistor, wherein each of said at least one memory transistorcomprises a source, a drain, and a channel; and a plurality of bit-linepillars, wherein each bit-line pillar of said plurality of bit-linepillars is directly connected to a plurality of said source or saiddrain, wherein said bit-line pillars are vertically oriented, andwherein said plurality of memory cells comprise a partially or fullymetalized source, and/or a partially or fully metalized drain.
 9. Thedevice according to claim 8, wherein each memory cell of said pluralityof memory cells comprises a charge trap memory, wherein said channelcomprises polysilicon, wherein said source and/or said drain comprisesmetal atoms, and wherein said metal atoms enable hot electronprogramming of said charge trap memory.
 10. The device according toclaim 8, wherein each of said memory transistors is directly connectedto at least one of said plurality of bit-line pillars.
 11. The deviceaccording to claim 8, wherein said channel is horizontally oriented andcomprises a channel width greater than 5 nm and less than 25 nm.
 12. Thedevice according to claim 8, wherein said plurality of memory cellscomprise a tunneling oxide thinner than 1 nm.
 13. The device accordingto claim 8, wherein said channel comprises a circular shape or anellipsoidal shape.
 14. The device according to claim 8, wherein said atleast one memory transistor is self-aligned to an overlaying anothersaid at least one memory transistor, both being processed following thesame lithography step.
 15. A 3D memory device, the device comprising: aplurality of memory cells, wherein each memory cell of said plurality ofmemory cells comprises at least one memory transistor, wherein each ofsaid at least one memory transistor comprises a source, a drain, and achannel; and a plurality of bit-line pillars, wherein each bit-linepillar of said plurality of bit-line pillars is directly connected to aplurality of said source or said drain, wherein said bit-line pillarsare vertically oriented, and wherein said channel comprises crystallizedpolysilicon.
 16. The device according to claim 15, wherein each memorycell of said plurality of memory cells comprises a charge trap memory,wherein said channel comprises polysilicon, wherein said source and/orsaid drain comprises metal atoms, and wherein said metal atoms enablehot electron programming of said charge trap memory.
 17. The deviceaccording to claim 15, wherein each of said memory transistors isdirectly connected to at least one of said bit-line pillars.
 18. Thedevice according to claim 15, wherein said plurality of memory cellscomprise a partially or fully metalized source, and/or a partially orfully metalized drain.
 19. The device according to claim 15, wherein atleast one of said plurality of said memory cells comprise a tunnelingoxide thinner than 1 nm.
 20. The device according to claim 15, whereinsaid at least one memory transistor is self-aligned to an overlayinganother said at least one memory transistor, both being processedfollowing the same lithography step.